Comparison of Low-Energy and Medium-Energy Collimators for Thyroid Scintigraphy with ¹²³I

CE credit: For CE credit, you can access the test for this article, as well as additional JNMT CE tests, online at https://www.snmmilearningcenter.org Complete the test online no later than March 2025. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 75% of the questions correctly to receive Continuing Education Hour (CEH) credit. Credit amounts can be found in the SNMMI Learning Center Activity. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test.¹²³I thyroid scintigraphy can be performed with either a low-energy or a medium-energy (ME) collimator. The high-energy photon emissions from ¹²³I cause septal penetration with scattered photons, which deteriorate image quality. The aim of this study was to evaluate the impact of collimator choice on ¹²³I thyroid scintigraphy in clinical practice. Methods: Forty-seven patients who underwent thyroid planar scintigraphy with both a low-energy, high-resolution (LEHR) collimator and a ME collimator were prospectively recruited using the same imaging protocol. Image quality, collimator sensitivity, and estimation of thyroid size were assessed between LEHR and ME collimators and were compared with thyroid ultrasonography as the gold standard. Results: Images acquired with the ME collimator demonstrated reduced scattered background noise, improved thyroid-to-background contrast, and increased sensitivity in the thyroid gland compared with images acquired by the LEHR collimator. Manual measurement of the thyroid length is more accurate using the ME collimator. Automatic estimation of the thyroid area using the same thyroid threshold is larger in ME collimator images than in LEHR collimator images. Conclusion: Compared with the LEHR collimator, the ME collimator generates cleaner ¹²³I thyroid scintigraphy images with less background noise and has higher collimator sensitivity for thyroid imaging. Different thyroid thresholds should be used to estimate the thyroid area and volume between low and ME collimators.